Hydrophobic silica particles possess physical properties that are useful in a number of applications requiring a high degree of dispersibility, including use in toner compositions, as antiblocking agents, as adhesion modifiers, and as polymer fillers. Untreated silica particles are hydrophilic due to the presence of silanol groups (Si-OH) on the surface of the untreated silica particles. By treating hydrophilic silica particles, the hydrophilic nature of the silica particles can be reduced, thereby imparting varying degrees of hydrophobicity to the particles.
Many different methods are known for treating the surface of silica particles. Some methods involve coating the particles with a silicone-type composition or other hydrophobic composition. Other methods involve reacting the surface silanol groups with a treating agent to effectively replace the hydrophilic silanol groups with other, hydrophobic, chemical groups. However, many treating agents are difficult to disperse in water, or tend to hydrolyze in water prior to replacing the surface silanol groups. Thus, the direct treatment of an aqueous dispersion of silica is often inefficient or difficult to achieve. As a result, these types of treatments are often acid-catalyzed reactions, or require the use of organic solvents.
Thus, a need still exists for simple and economical methods of preparing hydrophobic silica particles, especially methods that can be used to prepare hydrophobic silica directly from an aqueous dispersion of silica. The present invention provides such a method. These and other advantages of the invention will be apparent from the description of the invention provided herein.